Reports indicate that additions of fluoride to communal water supplies reduced significantly the incidence of dental caries. In a number of instances anticariogenicity has been shown to arise from retardation of fermentation of dietary carbohydrate by oral bacteria. The major problem in interpreting the effects of fluoride on bacterial metabolism is the lack of information related to the definition of the site of binding of fluoride, the type of microorganisms that bind fluoride, the quantity of fluoride bound by oral bacteria and the conditions under which fluoride binding occurs. It is to these fundamental problems mentioned above to which this investigation is being directed.